package string;

import java.util.Random;

public class CharAtDemo {
    public static void main(String[] args) {
        String str = "0123456789abcdefghijklmnopqrstuvwxyz";
        Random random = new Random();
        int len = str.length();
        for (int i = 0 ; i < 4 ; i++){
            int s = random.nextInt(len);
            char c = str.charAt(s);
            System.out.print(c);
        }
    }
}
